This invention relates to non-destructive testing methods and techniques and in particular to non-destructive, in situ-monitoring of semiconductors during laser annealing process.
Impurities introduced into a semiconductor sample by ion-implantation produce damage in the crystal which must subsequently be removed by thermal treatment in a furnace or by laser annealing. The annealing serves to incorporate the implanted ions into electrically active sites and to reduce defect traps to the point where carrier lifetimes and mobilities have useful values. In order to ascertain that impurity activation has been achieved, the technique commonly used consists of the fabrication and characterization of a MOSFET or a MOS capacitor. The turn-on or inversion voltage of these devices or the channel conductance of the FET at pre-set voltage levels can be used as measures of impurity activation. However, these techniques are destructive in that several wafer processing steps are needed for the fabrication of the test structures; as a result, after the test for implant activation, the wafer cannot be used for making useful devices.
Accordingly, there currently exists the need for a non-destructive and rapid method of monitoring the adequacy of the thermal cycle during semiconductor wafer processing. Such a method is highly desirable since the wafer could either be qualified for use in device fabrication or be further annealed. The present invention is directed toward providing such a method.